I'm looking at an engine that was advertised as a 1966 235, but I believe '62 was the last year for 235s. The owner furnished me these numbers:

3836848 GM30. Bottom of motor: CON4D29R GM16.

I've searched the Archives and used the various lists of casting numbers, etc, and come up with:

235 built April 2, 1959 with 848 cylinder heads used between 58 and 62.

Is that correct? What does the "R" mean?

Thanks for any help